1. Field of the Invention
The present invention relates to a tape reel equipped with a hub having driven teeth capable of meshing with driving teeth, a cartridge case equipped with such tape reel, and an information recording medium equipped with such cartridge case.
2. Description of the Related Art
As one example of this type of information recording medium, a single-reel-type tape cartridge used for backing up data and the like is known. With this type of tape cartridge, driven teeth that are ring-shaped are disposed on the base plate of the hub of a tape reel, with driving teeth of a drive apparatus meshing with the driven teeth so that the tape reel can be rotated (driven) by the drive apparatus. Here, to cause the tape reel to rotate smoothly, the tape reel should preferably be fabricated so that every tooth surface of the teeth that compose the driven teeth contacts every tooth surface of the teeth that compose the driving teeth. However, since the shape of the driven teeth is complex, when the tape reel is fabricated by injection molding, due to the characteristics of injection molding, extremely slight differences in the dimensions of the individual teeth composing the driven teeth are caused by slight changes in the molding conditions and the like. This means that it is extremely difficult to fabricate the tape reel so that all of the tooth surfaces are in contact. Accordingly, with such tape cartridge, when the driven teeth of the tape reel and the driving teeth of the drive apparatus mesh, the driven teeth and the driving teeth are in contact at certain positions and apart at other positions, resulting in the risk of surging occurring when the tape reel is rotated.
As a technique for solving the above problem, the tape cartridge disclosed in Japanese Laid-Open Patent Publication No. 2005-209277 is known. With this tape cartridge, gear teeth (driven teeth) in the shape of a ring that are formed on a lower surface of a base plate of the tape reel are composed of first gear teeth and second gear teeth with respectively different heights. The second gear teeth are formed with greater teeth heights than the first gear teeth, and as shown in FIG. 6 of the publication, two second gear teeth are disposed in each of three regions produced by dividing a circle. As a result, when the gear teeth and the driving teeth of a drive apparatus (tape drive) mesh, only the second gear teeth with the greater heights engage the driving teeth. Accordingly, with this tape cartridge, by precisely setting the dimensions of the low number of second gear teeth, it is possible to prevent surging from occurring when the tape reel rotates.
By investigating the tape cartridge described above, the present inventor discovered the following problem. With the above tape cartridge, by limiting the gear teeth of the tape reel that engage the driving teeth of the drive apparatus to the low number of second gear teeth and precisely setting the dimensions of the second gear teeth, surging of the tape reel can be prevented more reliably. However, as long as the tape reel is fabricated by injection molding, it is still extremely difficult to fabricate the tape reel so that the second gear teeth that are complex in form have the set dimensions. Accordingly, with this tape cartridge also, there is the problem that surging may occur when the tape reel rotates.